Clippy lints / Nursery
Clippy lint · Nursery · checked with Clippy 0.1.99
clippy::trailing_empty_array: trailing zero-sized array in a struct which is not marked with a `repr` attribute
What it meansDisplays a warning when a struct with a trailing zero-sized array is declared without a repr attribute. It is in the nursery group and off by default.
What you see
warning: trailing zero-sized array in a struct which is not marked with a `repr` attribute --> main.rs:3:1 | 3 | / struct RarelyUseful { 4 | | some_field: u32, 5 | | last: [u32; 0], 6 | | } | |_^ | = help: consider annotating `main::RarelyUseful` with `#[repr(C)]` or another `repr` attribute = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#trailing_empty_array = note: `-W clippy::trailing-empty-array` implied by `-W clippy::nursery`
Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.
Does it matter?
Zero-sized arrays aren’t very useful in Rust itself, so such a struct is likely being created to pass to C code or in some other situation where control over memory layout matters (for example, in conjunction with manual allocation to make it easy to compute the offset of the array). Either way, #[repr(C)] (or another repr attribute) is needed.
New lints still being finished. Off by default and may have false positives.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Flagged
struct RarelyUseful {
some_field: u32,
last: [u32; 0],
}
Write this instead
#[repr(C)]
struct MoreOftenUseful {
some_field: usize,
last: [u32; 0],
}
Turn it off, or on
It is off by default. To use it, set it to warn or deny:
Whole crate (Cargo.toml)
[lints.clippy]
trailing_empty_array = "warn"In code
#![warn(clippy::trailing_empty_array)]One run
cargo clippy -- -W clippy::trailing-empty-arrayThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Clippy's own documentation
What it does
Displays a warning when a struct with a trailing zero-sized array is declared without a repr attribute.
Why is this bad?
Zero-sized arrays aren’t very useful in Rust itself, so such a struct is likely being created to pass to C code or in some other situation where control over memory layout matters (for example, in conjunction with manual allocation to make it easy to compute the offset of the array). Either way, #[repr(C)] (or another repr attribute) is needed.
Example
struct RarelyUseful {
some_field: u32,
last: [u32; 0],
}
Use instead:
#[repr(C)]
struct MoreOftenUseful {
some_field: usize,
last: [u32; 0],
}
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
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All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::redundant_cloneChecks for a redundant clone() (and its relatives) which clones an owned value that is going to be dropped without further useRead it next →Did this answer your question?